1. Field of the Invention
The present invention relates to an apparatus and method for reducing the size of solid materials in a substance. The invention has particular advantages associated with processing of sediment accumulated in a storage area for paper pulping byproducts, such as black liquor.
2. Description of Related Art
Pulp is the primary raw material used in the production of most, if not all, paper products. To manufacture pulp, reduced-size pieces of cellulose containing materials, usually wood, are exposed to a liquid solution, sometimes referred to as xe2x80x9cwhite liquorxe2x80x9d. The white liquor dissolves certain organic components of the wood, such as lignin (i.e., tree sap), and the resulting cellulosic materials are used as pulp.
Black liquor is a by-product of the pulping process. Black liquor contains considerable amounts of the dissolved organic materials, along with spent dissolving agents and other substances, such as wood fibers, water, and dirt. Because black liquor is loaded with organic materials and some relatively volatile substances, it has a heat value in BTUs that is approximately half the heat value of #6 oil. At some pulping facilities, black liquor is burned and the heat from this combustion is used in the manufacture of additional pulp or in a paper making process. Alternatively, the black liquor is treated to remove some of its dissolved substances and this treated liquor- is reused for further pulp manufacture.
Regardless of whether black liquor is burned or reused, it is usually stored for a period of time in one or more storage tanks or lagoons at a pulping facility. During storage, heavy solids, pulp residue, and lignin settle in these storage areas, and over time the sediment accumulates to an extent that requires cleaning. In a typical cleaning procedure, excess liquid is drained from the storage area and the sediment is shoveled out either manually or through the use of construction equipment. Sometimes the sediment is vacuumed into a truck similar to a dump truck.
After black liquor sediment is removed from a storage area, it usually has relatively large clumps of solid material that are unsuitable for use as fuel or for recycling. Currently, there is no effective way of processing black liquor sediment so that it can be reused. Accordingly, black liquor sediment is normally dumped in landfills. However, landfill disposal of black liquor sediment has a number of drawbacks.
Current landfill regulations require black liquor sediment to be neutralized from its relatively high PH of 10-12 to a more neutral PH of 7-8 before it is disposed. Black liquor sediment is neutralized by mixing it with a neutralizing agent that is normally added in a one to one ratio with the black liquor sediment. For example, 100 tons of black liquor sediment is mixed with 100 tons of neutralizing agent before landfill disposal. This is a relatively expensive process that requires purchasing a substantial amount of neutralizing agent, transporting both the sediment and the neutralizing agent to the landfill site, and filling a considerable amount of landfill space. In addition, the disposed black liquor sediment contains a significant amount of potential combustion heat value that is never used.
In light of the foregoing, there is a need for processing sediment that includes byproducts of paper pulping.
Accordingly, the present invention is directed to a method and apparatus that substantially obviate one or more of the limitations of the related art. To achieve these and other advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention may include a method of processing sediment accumulated in a storage area for containing paper pulping byproducts. Such a method includes conveying the sediment from the storage area to a tank. In the tank, clumps of the sediment are shredded to reduce their size and these reduced-size clumps are removed from the tank. Preferably, the reduced-size clumps are capable of being used in a facility that produces pulp and/or a facility that produces paper.
In an aspect of the invention, the sediment may be black liquor sediment and the clumps removed from the tank may be in a slurry form that is capable of being burned to provide heat that can be used in another process.
In another aspect, the method may include detecting at least one of the amount of solids in the slurry and the amount of liquid in the slurry, and adding liquid to the tank. Such a method may also include controlling at least one of the flow of liquid to the tank and the flow of the sediment to the tank based on at least one of the detected amount of solids and the detected amount of liquid.
In a further aspect, the slurry may be passed through a grinder to grind any relatively larger-size solid substances in the slurry.
In yet another aspect, flow rate of the slurry may be detected and information regarding the flow rate is recorded.
In an even further aspect, the shredding of the sediment may include rotating at least one blade in an interior of the tank. During rotation of the blade, a tip of the blade preferably moves adjacent to at least one shearing element located along an inner surface of the tank. This shears clumps of the sediment located between the blade and the shearing element.
In a preferred practice of the invention, the tank is mounted on a mobile wheeled chassis, and the method further includes transporting the tank to another storage area after removal of at least a substantial amount of sediment from the initial storage area.
Additionally, the present invention may include an agitation apparatus including at least one shearing element provided on an interior surface of the tank. The shearing element may be located in the tank such that when the blade rotates, a tip of the blade passes adjacent to the shearing element to shear solid substances between the blade and the shearing element. In a preferred embodiment, the shearing element may be at least one bar extending along the longitudinal axis of the tank.
In an additional aspect, the apparatus may include a solid/liquid detector configured to detect the amount of solids and/or the amount of liquid in the substances removed from the tank. Structure is provided for controlling flow of the substances into the tank based upon the detected amount of liquid and/or the detected amount of solids.
Optionally included in the apparatus are a discharge pump configured to remove substances from the tank, a grinder for grinding the removed substances, and/or a flow rate detector configured to detect the flow rate of removed substances.
In an even further aspect, at least one inflow conduit and at least one vacuum pump are coupled to the tank. The vacuum pump provides a vacuum force in the conduit. Optionally, a flow valve is flow coupled to the inflow conduit.
While the invention has particular applicability in recycling pulping by-products, it may be used to process many different products having liquid and solid/semi-solid constituents. Thus, it is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.